Oxygen precipitation in nitrogen doped Czochralski silicon wafers. I. Formation mechanisms of near-surface and bulk defects J. Appl. Phys. 96, 3255 (2004) Heterogeneous iron precipitation in silicon was studied experimentally by measuring the gettering efficiency of oxide precipitate density of 1 ϫ 10 10 cm −3 . The wafers were contaminated with varying iron concentrations, and the gettering efficiency was studied using isothermal annealing in the temperature range from 300 to 780°C. It was found that iron precipitation obeys the so-called s-curve behavior: if iron precipitation occurs, nearly all iron is gettered. For example, after 30 min annealing at 700°C, the highest initial iron concentration of 8 ϫ 10 13 cm −3 drops to 3 ϫ 10 12 cm −3 , where as two lower initial iron concentrations of 5 ϫ 10 12 and 2 ϫ 10 13 cm −3 remain nearly constant. This means that the level of supersaturation plays a significant role in the final gettering efficiency, and a rather high level of supersaturation is required before iron precipitation occurs at all. In addition, a model is presented for the growth and dissolution of iron precipitates at oxygen-related defects in silicon during thermal processing. The heterogeneous nucleation of iron is taken into account by special growth and dissolution rates, which are inserted into the Fokker-Planck equation. Comparison of simulated results to experimental ones proves that this model can be used to estimate internal gettering efficiency of iron under a variety of processing conditions.

Iron detection in polished and epitaxial silicon wafers using generation lifetime measurements

In order to achieve a better understanding of the behaviour of copper in p-type silicon, studies of the recombination of copper were carried out by the microwave photoconductive decay measurement method (µPCD) using high-intensity bias light. It was observed that in the presence of small oxygen precipitates, high-intensity light could be used to activate precipitation of interstitial copper. It is suggested that high-intensity light changes the charge state of interstitial copper from positive to neutral, which enhances the precipitation. The precipitation follows Ham's kinetics and results in an increase in the recombination rate, which is detectable even with very low copper concentrations. This phenomenon can be used to detect low levels of copper contamination by the µPCD method. In addition, it was observed that out-diffusion as well as in-diffusion of interstitial copper could be affected by an external corona charge. Thus, it is suggested that copper atoms do not form stable bonds at the Si-SiO 2 interface after out-diffusion from bulk silicon.

Articles you may be interested inA model is presented for the growth and dissolution of iron precipitates at oxygen-related defects in silicon during thermal processing. The heterogeneous nucleation of iron is taken into account by special growth and dissolution rates, which are inserted into a set of modified chemical rate equations. This approach allows us to calculate the size distribution of iron precipitates and the residual iron concentration. By comparing the simulated results with experimental ones, it is proven that this model can be used to estimate the internal gettering efficiency of iron under a variety of processing conditions.

We have studied internal gettering efficiency of iron in silicon by Deep Level Transient Spectroscopy (DLTS) and standard lifetime-methods (SPV, PCD). Conventional high-low-high anneals were performed to produce a series of wafers with varying denuded zone (DZ) width and oxygen precipitation density. The wafers were intentionally iron contaminated to a level of about 3-5 * 10 13 cm −3. After contamination the wafers were annealed at 900 • C and then slowly cooled to 850, 800, 750, 700 or 600 • C. After cooling the remaining interstitial iron concentration was measured by SPV,-PCD and DLTS. The experimental results are compared with simulations. Our results indicate that with this contamination level, the gettering is effective only at temperatures below 750 • C when iron is supersaturated over a factor of twenty. For temperatures above 750 • C the gettering is limited by iron precipitation in the bulk.